Extensive co-existence of neuropeptides in the rat visual cortex.

The peroxidase-antiperoxidase immunohistochemical technique has been used to examine the co-existence of peptides within individual neurons of the rat visual cortex. Pairs of consecutive paraffin sections were stained alternately for 2 of the 4 peptides: somatostatin (SRIF), vasoactive intestinal polypeptide (VIP), cholecystokinin (CCK) and neuropeptide Y (NPY). Analysis revealed the co-existence of SRIF with VIP, CCK and NPY and between VIP and CCK. These results show that the co-localization of neuropeptides in cortical neurons is more widespread than previously demonstrated.